This invention relates to an improved method for the detoxification of liquid or solid materials and, more specifically, to the molecular conversion of such contaminants into less hazardous substances by the use of ultrasonic energy and chemical reagents.
Ultrasonic energy is known as a means to effect various physical and chemical changes in compounds. In particular, ultrasonic energy may be used as a tool to break or alter chemical bonds for the initiation of reactions or to boost existing reactions which otherwise occur more slowly. Uses of and theoretical mechanisms for the application of ultrasonic energy to effect chemical changes has been discussed in Boucher, "Sonochemistry at Low and High Ultrasonic Frequencies", Progress Report, March, 1970, Vol. 15, No. 3; Weissler, "Sonochemistry: The Production of Chemical Changes with Sound Waves", J. Acustica. Soc. of America, Vol. 25, No. 4 (July, 1953), pp. 651-657; and U.S. Pat. No. 4,477,357 to Sittenfield, which are all incorporated herein by reference.
It is theorized that the mechanism by which ultrasonic waves produce chemical change involves the phenomenon of cavitation, which is the formation and subsequent rapid collapse of cavities (bubbles in liquid) which are filled with the gas or vapor that may be present in the material itself or in the surrounding atmosphere. The collapse produces very large amplitude shock waves with an attendant rapid and substantial increase in temperature. Particles, in gas, liquid or solid states, or other types of discontinuities, may act as nuclei for the initiation of cavitation.
Ultrasonic energy in wave form may be used to form and collapse the cavities in a cyclic nature, which cycling may be used to create what is known as cavity (or bubble) resonant size. When the cavities reach resonant size, the collapse of the cavities occurs at such a rate that high local pressures of about 20,000 atmospheres and temperatures of about 10,000 Kelvin are attained.
Although high temperatures can be achieved, the high temperatures are transitory. However, the rise in temperature can be sustained for sufficient time to initiate a desired chemical change which otherwise is less likely to occur under standard temperature and pressure conditions.
It is theorized that the rise in temperature initiates the formation of free radicals by causing disassociation of molecular bonds of materials being treated. The free radicals may then react with other molecules present to form additional free radicals, thus propagating a chain reaction. Free radicals may also combine to terminate the chain reaction by forming new molecules which are either more desirable (less toxic) or which may be more readily extracted (than the unconverted contaminant) from the material being treated.
Yield of the desired chemical reactions or changes effecting detoxification is directly proportional to the intensity of cavitation, which cavity intensity is itself proportional to the amplitude of the cycling cavity size. The amplitude of the cavity size is itself further dependent upon medium viscosity (the higher the viscosity of the reactant medium, the lower the amplitude and the lower the pressure exerted by collapsing cavities) and is also directly proportional to the amplitude of the transducer surface that creates the ultrasonic wave emitted into the medium. The yield is, yet further, directly proportional to the chemical activity of the toxic materials in the medium being treated.
Ultrasonic waves in the lower portion of the ultrasonic frequency range, usually about twenty (20) KHz, are generally used because, at such frequencies, the resonant cavity size for typical materials treated is large, causing cavity collapses with greater force compared to that generated by collapse of smaller cavities produced by higher frequency ultrasonic waves.
Although subjection of contaminants to ultrasonic energy, without regard to the yield influencing factors that are discussed above, can result in some cleavage and detoxification (e.g. dehalogenation of an aromatic ring), the detoxification yield may not be optimum.
Further, even though it is known that the addition of certain alkaline agents, such as those disclosed in U.S. Pat. No. 4,477,357, to a treated medium is claimed to improve detoxification yield, such alkaline agents therein disclosed do not furnish optimum yields. Other reagents have been discovered which either offer better yields or are more readily available or are better suited for particular detoxification applications.